Hydraulic actuating systems



June 23, 1970 R. E. J. SKEATES 3,516,445

HYDRAULIC ACTUATING SYSTEMS Filed Feb. 4!, 1969 2 Sheets-Sheet 1 June23, 1970 R. E. J. SKEATES 3,515,445

HYDRAULIC ACTUATING SYSTEMS Filed Feb. 4, 1969 2 Sheets-Sheet 2 UnitedStates Patent O 3,516,445 HYDRAULIC ACTUA'HNG SYSTEMS Ronald E. J.Skeates, Ilford, England, assignor to The Plessey Company Limited,Iiford, England, a British company Filed Feb. 4, 1969, Ser. No. 796,345Claims priority, application Great Britain, Feb. 7, 1968, 6,024/ 68 Int.Cl. F16k 11/07, 11/10, 23/00 US. Cl. 137-62567 3 Claims ABSTRACT OF THEDISCLOSURE A hydraulic actuating arrangement in which a spool valvecomprises a spool slidable in a bore in the body of the actuator, thespool being provided with a peripheral groove which, at least in theneutral position of the spool is trained so that leakage between thespool and said bore is intercepted by said groove and prevented fromreaching the associated actuator (not shown). Such an arrangement may beconveniently used in digger or loading equipment to prevent creepage ofthe associated actuator members.

This invention relates to hydraulic actuating systems of the kind inwhich a single positive-displacement hydraulic power source is madeavailable for the selective utilisation in a number of hydraulicservices, each having a separate spool valve by inter-connecting thesespool valves by a transfer passage which passes from a pressure inlet inseries through a port of each spool valve which is open when the valvespool is in an inoperative position, to reach a lowpressure return port,so that when each spool valve is in its inoperative position, thepressure source is unloaded via the transfer passage, while the transferpassage is closed to cause a pressure build-up when any spool is movedto an operative position, each spool valve having a pressure portcommunicating with the said pressure inlet via a nonreturn valve, one ormore service ports, and one or more return ports communicating with apoint at low pressure, the high-pressure, service, and low pressureports of each valve being isolated by lands of the valve spool when thelatter is in its inoperative position.

It will be readily appreciated that when any one of the valve spools isin an operative position, the pressure ports of all valves will bepressurised, and therefore if the unit controlled by this one spooloperates against a high pressure, pressure is liable to leak in theother valves past the intervening lands of their respective valve spoolstowards the service ports of these other valves, and that if there isany asymmetry of this leakage, this may lead to creeping of a servicewhose valve spool is in its inoperative position. In many applicationssuch creepage is objectionable, one example being loader equipment anddigger equipment respectively mounted on the front and rear of avehicle, an arrangement in which it is usual to employ the loader toanchor the vehicle during digging operations.

The present invention has for an object to provide a safeguard againstsuch creeping of non-selected services. According to the invention inthe valve assembly of hydraulic actuating systems of the kind specified,the valve spool of a service to be protected against creepage isprovided with a peripheral groove which in the inoperative position ofthe valve spool faces the land separating the pressure port and theservice port of the valve housing for the service controlled by thevalve spool in question, this groove being, at least in the inoperativeposition of the spool, drained to a point at low pressure so thatleakage from the pressure port towards the service port of the valve isintercepted by the groove and thus prevented from reaching the serviceport of the valve.

Patented June 23, 1970 "ice One embodiment of the invention will now bedescribed with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic plan view showing part of the hydraulicequipment and including a section of the valve assembly, and

FIG. 2 is an elevation, partly in section on line A-A of FIG. 1.

Referring now to the drawings, hydraulic liquid from a reservoir T ispumped via a positive-displacement pump P to a transfer passage 1, whichis sub-divided by lands 6a, 6b and 60, respectively co-operating withvalve spools 3a, 3b and 3c, into series-connected portions 1a, 1b, 1cand 1d, the latter being drained to the reservoir T by a return line 4,which also communicates with two low-pressure ports 21 for each spoolvalve 3a, 3b and 30 respectively arranged at each side of the transferpassage 1. The inlet of the transfer passage 1 further communicates witha pressure gallery 9, see FIG. 2, which is connected to a pair ofannular pressure ports 12 for each valve spool via a check valve 10 andbranch passage 11. Arranged at each side of the transfer passage, abouthalf-way between the pressure port 12 and the return port 21 for eachvalve spool 3, is a service port 14 and 24 respectively, each serviceport 14 and 24 being faced by an annular port 16 or 26 respectively inthe valve spool which, as the valve spool is moved to one or the otherside from its illustrated inoperative central position, connects theservice port with either the pressure port 12 or the low-pressure port21 in a well known manner so that displacement of a spool 3 towards theleft will connect its right-hand service port 14 to the associatedpressure port 12 while venting the left-hand service port 24 to alow-pressure port 21 and vice versa thus causing operation of theassociated service in one direction or the other according to thedirection in which the valve spool has been displaced. In theillustrated embodiment it has been assumed that while slight creepage ofthe service controlled by valve spool 3a is not particu larlyobjectionable, such creepage cannot be permitted in the case of theservice controlled by valves 3b and 30 respectively. In order to preventsuch creepage in each of the last-mentioned valves along the lands 7 and8 which, in cooperation with lands 15 and 25 of the valve housing 2isolates, in the inoperative position of these valves, their pressureports 12 from their service ports 14 and 24, a circumferential groove 17is provided in each of the lands 7 and 8 of these valve spools at apoint of their length which, when the valve spool is in its inoperativeposition, faces the land 15 or 25 of the valve housing which separatesthe pressure port 12 from the service port 14 or 24, and each of thesegrooves communicates, by radial bores 18 and a longitudinal bore 19extending along the axis of the spool, with radial bores 20 which whenthe valve is in this inoperative position, open into one of thelow-pressure ports 21, so that any liquid which may leak from one of thepressure ports 12 along one of the lands 7 or 8 of either valve spool 3bor 3c towards the adjacent service port 14 or 24 will be intercepted bythe groove 17 and is via the low-pressure port 21 returned to thereservoir tank T.

This arrangement is clearly of particular advantage in cases in whichone of the services, for example that controlled by valve spool 3a, isliable to require a very high operating pressure while one or more otherservices, for example those controlled by spools 3b and 3c, are normallyrequired to be held, during the operation of this highpressure service,in a preset position to effect a holding operation which is unlikely toproduce high pressures in their operating units.

The disposition position of the radial bores 18 and 20 has been sochosen as to prevent the creation of a shortcircuit bleed through thesebores and the axial bore 19,

between the service ports 14, 24 and their respectively associatedpressure and return ports 12 and 21. Thus it will be seen that when avalve spool is moved to the right of FIG. 1, its bores 20, which in theneutral position communicate with the low-pressure port 21, will beblanked off by the land 23 of the valve housing which separates thisport from the adjacent service port 24 before the groove 17 reaches theassociated pressure port 12, While when the valve is moved to the left,the groove 17 in land 8 will remain in co-operation with the land 25that separates service port 24 from pressure port 12, until the radialbores 20 at the left-hand side of the spool become isolated fromlowpressure port 21 by the land 27 provided beyond that port. The samearrangements apply to the right-hand side of each of the spools 3b and30 when the spool is moved to the left and to the right respectively.

What is claimed is:

1. A valve assembly for hydraulic actuating equipment of the kindhereinabove specified, wherein the valve spool of a service to beprotected against creepage is provided with a peripheral groove which inthe inoperative position of the valve spool faces the land separatingthe pressure port and the service port of the valve housing for theservice controlled 'by the valve spool in question, and means forconnecting said groove to a point at low pres sure so that leakage fromthe pressure port towards the service port of the valve is interceptedby the groove and thus prevented from reaching the service port of thevalve.

2. A valve assembly as claimed in claim 1, wherein said valve spool hasan inoperative position and at least one operative position, said meansfor connecting said groove being so constructed as to be operative onlywhen the valve spool is in said inoperative position.

3. A valve assembly as claimed in claim 1, including a valve housinghaving a bore in which the valve spool slides, at least one land forminga wall portion of said bore, at least one low-pressure port and at leasttwo further ports including at least one pressure port and at least oneservice port, all said ports opening into said bore, wherein the valvespool is provided with an axial passage and with two axially spacedradial bores intersecting said passage and respectively leading to thegroove and to a point at the surface of the spool which faces suchlow-pressure port when the spool is in its inoperative position butfaces, and is blanked oil? by, such land when the groove is open to suchfurther pressure port of the valve housing.

References Cited UNITED STATES PATENTS 2,486,087 10/1949 Wright137-596.13 3,262,467 7/1966 Stacey 137625.69 XR 3,429,341 2/ 1969Sochting 137-625.68

HENRY T. KLINKSIEK, Primary Examiner US. Cl. X.R. 1373l2

